1. Field of the Invention
The present invention relates to a spin-valve thin-film magnetic element including a free magnetic layer and laminates of pinned magnetic layers and antiferromagnetic layers formed on two surfaces of the free magnetic layer, and to a method for making the spin-valve thin-film magnetic element.
2. Description of the Related Art
Magnetoresistive magnetic heads are classified into anisotropic magnetoresistive (AMR) heads provided with elements having anisotropic magnetoresistive effects and giant magnetoresistive (GMR) heads provided with elements having giant magnetoresistive effects. An AMR head has a single layer structure of a magnetic element exhibiting a magnetoresistive effect. In contrast, a GMR head is provided with a multi-layered element composed of a plurality of layers exhibiting an anisotropic magnetoresistive effect. Several structures have been proposed to produce giant magnetoresistive effects. A spin-valve thin-film magnetic element has a simple structure and a high rate of change of resistance to a weak external magnetic field. Spin-valve thin-film magnetic elements are classified into single spin-valve thin-film magnetic elements and dual spin-valve thin-film magnetic elements.
FIGS. 12 and 13 are schematic cross-sectional views of a conventional spin-valve thin-film element.
Shielding layers are formed above and below the spin-valve thin-film element with gap layers therebetween, and a GMR head for reading is composed of the spin-valve thin-film element, the gap layers, and the shielding layers. An inductive head for recording may be deposited on the GMR head for reading.
The GMR head and the inductive head are provided at a trailing end of a floating slider and constitute a thin-film magnetic head. The GMR head detects recorded magnetic fields on magnetic recording media, such as hard disks. In FIGS. 12 and 13, a magnetic recording medium moves in the Z direction and a fringing magnetic field is generated in the Y direction from the recording magnetic medium.
The spin-valve thin-film magnetic element 3 shown in FIG. 12 is a so-called dual spin-valve thin-film magnetic element in which a nonmagnetic conductive layer, a pinned magnetic layer, and an antiferromagnetic layer are deposited on each of two surfaces of a free magnetic layer.
The dual spin-valve thin-film magnetic element includes two groups of triple-layer configurations, each including a free magnetic layer, a nonmagnetic conductive layer, and a pinned magnetic layer. Thus, this element has a large rate of change of resistance compared to a single spin-valve thin-film magnetic element having a single group of the triple-layer configuration including the free magnetic layer, the nonmagnetic conductive layer, and the pinned magnetic layer, and can be used in high-density recording.
In the spin-valve thin-film magnetic element 3 shown in FIGS. 12 and 13, an underlying layer 10, a second antiferromagnetic layer 11, a second pinned magnetic layer 12, a nonmagnetic conductive layer 13, a free magnetic layer 14 composed of Co films 15 and 17 and a NiFe alloy film 16, a nonmagnetic conductive layer 18, a first pinned magnetic layer 19, a first antiferromagnetic layer 20, and a protective layer 21 are deposited in that order from the bottom of the drawings.
As shown in FIG. 13, biasing layers 130 and conductive layers 131 are formed on two sides of the laminate over the underlying layer 10 to the protective layer 21.
The first and second pinned magnetic layers 19 and 12, respectively, are formed of, for example, a Co film, a NiFe alloy, a CoNiFe alloy, or a CoFe alloy.
The first and second antiferromagnetic layers 20 and 11, respectively, are formed of a PtMn alloy, an XMn alloy wherein X is at least one metal selected from Pd, Ir, Rh, Ru and Os, or a PtMnZ alloy wherein Z is at least one element selected from Pd, Ir, Rh, Ru, Os, Au, Ag, Cr, Ni, Ne, Ar, Xe and Kr.
The first pinned magnetic layer 19 and the second pinned magnetic layer 12 in FIG. 12 are magnetized at interfaces with the first and second antiferromagnetic layers 20 and 11, respectively, by exchange anisotropic magnetic fields by exchange coupling (unidirectional exchange coupling magnetic fields), and the magnetization vectors are fixed in the Y direction in the drawing, that is, a direction (height direction) away from the recording medium.
The free magnetic layer 14 is aligned in a single-domain state by a magnetic flux from the biasing layers 130, and the magnetization is aligned in the X direction in the drawing, which is perpendicular to the magnetization vector of the first and second pinned magnetic layers 19 and 12, respectively.
Since the free magnetic layer 14 is aligned to a single-domain state by the biasing layers 130, the generation of Barkhausen noise is avoidable.
In the spin-valve thin-film magnetic element 3, when stationary currents flow from one conductive layer 131 to the free magnetic layer 14, the nonmagnetic conductive layers 18 and 13, respectively, and the first and second pinned magnetic layers 19 and 12, and when a fringing magnetic field is applied in the Y direction from the magnetic recording medium, which moves in the Z direction, the magnetization of the free magnetic layer 14 changes from the X direction to the Y direction. Such a change in magnetization vector in the free magnetic layer 14 causes a change in electrical resistance of the element in relation to the magnetization vector of the first and second pinned magnetic layers 19 and 12, respectively. The fringing magnetic field from the magnetic recording medium is detected as a change in voltage based on the change in electrical resistance.
In the production of this spin-valve thin-film magnetic element 3, individual layers from the underlying layer 10 to the protective layer 21 are deposited in that order, and are annealed in a magnetic field to generate exchange anisotropic fields at an interface between the first pinned magnetic layer 19 and the first antiferromagnetic layer 20 and at an interface between the second pinned magnetic layer 12 and the second antiferromagnetic layer 11 so that the first and second pinned magnetic layers 19 and 12, respectively, have the same magnetization vector (Y direction in the drawing).
In the conventional spin-valve thin-film magnetic element 3, as shown in FIG. 14, it is preferable that the magnetization vector (H3) of the free magnetic layer 14 be perpendicular to the magnetization vectors (H1 and H2) of the first and second pinned magnetic layers 19 and 12, respectively, when an external magnetic field is not applied from the recording medium. However, dipolar magnetic fields (H4 and H5) leaking from the first and second pinned magnetic layers 19 and 12, respectively, enter the free magnetic layer 14 from the opposite direction to the Y direction. These dipolar magnetic fields (H4 and H5) tilt the magnetization vector (H3) toward the vector (H6) opposite to the Y direction, and thus preclude biasing adjustment for orienting the magnetization vector of the free magnetic layer 14. As a result, the magnetization vector (H6) of the free magnetic layer 14 cannot be perpendicular to the magnetization vectors (H1 and H2) of the first and second pinned magnetic layers 19 and 12, respectively, and the regenerated waveform is inevitably asymmetric.
It is an object of the present invention to provide a spin-valve thin-film magnetic element which has no tilt of the magnetization vector of a free magnetic layer and can suppress asymmetry of the regenerated waveform.
It is another object of the present invention to provide a thin-film magnetic head having the spin-valve thin-film magnetic element.
It is a still another object of the present invention to provide a method for making the spin-valve thin-film magnetic element.
In a first aspect of the present invention, a spin-valve thin-film magnetic element includes a substrate, a laminate formed on the substrate, biasing layers, and conductive layers. The laminate includes a free magnetic layer; a first nonmagnetic conductive layer, a first pinned magnetic layer and a first antiferromagnetic layer deposited on the upper surface, away from the substrate, of the free magnetic layer; a second nonmagnetic conductive layer, a second pinned magnetic layer and a second antiferromagnetic layer deposited on the lower surface, near the substrate, of the free magnetic layer. The biasing layers orients the magnetization vector of the free magnetic layer in a direction perpendicular to the magnetization vector of the pinned magnetic layers, and the conductive layers supplies a sensing current to the free magnetic layer. The first antiferromagnetic layer adjoining the first pinned magnetic layer fixes the magnetization vector of the first pinned magnetic layer in one direction. The second antiferromagnetic layer adjoining the second pinned magnetic layer fixes the magnetization vector of the second pinned magnetic layer in a direction antiparallel to the magnetization vector of the first pinned magnetic layer. In addition, the first and second antiferromagnetic layers are composed of an alloy comprising Mn and at least one element selected from the group consisting of Pt, Pd, Ir, Rh, Ru, Os, Au, Ag, Cr, Ni, Ne, Ar, Xe and Kr.
This alloy contributes to generation of a large exchange anisotropic magnetic field which securely fixes the magnetization vectors of the first and second pinned magnetic layers. Moreover, the exchange anisotropic magnetic field has excellent temperature dependence. Thus, the resulting spin-valve thin-film magnetic element has superior linear response in magnetoresistive effects.
In an embodiment of the spin-valve thin-film magnetic element, the free magnetic layer comprises a nonmagnetic interlayer, and a first free magnetic layer and a second free magnetic layer formed on the two surfaces of the nonmagnetic interlayer, and the first free magnetic layer and the second free magnetic layer are antiferromagnetically coupled with each other so that the magnetization vectors of the first free magnetic layer and the second free magnetic layer are antiparallel to each other.
Preferable, the first antiferromagnetic layer comprises an alloy represented by the formula:
XmMn100xe2x88x92m
wherein X is at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Ru and Os, and m is in a range of 52 atomic percent to 60 atomic percent.
Preferably, the second antiferromagnetic layer comprises an alloy represented by the formula:
XmMn100xe2x88x92m
wherein X is at least one metal selected from the group consisting of Pt, Pd, Ir, Rh, Ru and Os, and m is in a range of 48 atomic percent to 58 atomic percent.
Alternatively, the first antiferromagnetic layer may comprise an alloy represented by the formula:
PtqMn100xe2x88x92qxe2x88x92nZn
wherein Z is at least one element selected from the group consisting of Au, Ag, Cr, Ni, Ne, Ar, Xe and Kr, and q and n satisfy the relationships (52 atomic percent)xe2x89xa6(q+n))xe2x89xa6(60 atomic percent) and (0.2 atomic percent)xe2x89xa6nxe2x89xa6(10 atomic percent).
Alternatively, the second antiferromagnetic layer may comprise an alloy represented by the formula:
PtqMn100xe2x88x92qxe2x88x92nZn
wherein Z is at least one element selected from the group consisting of Au, Ag, Cr, Ni, Ne, Ar, Xe and Kr, and q and n satisfy the relationships (48 atomic percent)xe2x89xa6(q+n)xe2x89xa6(58 atomic percent) and (0.2 atomic percent)xe2x89xa6nxe2x89xa6(10 atomic percent).
Alternatively, the first antiferromagnetic layer may comprise an alloy represented by the formula:
PtqMn100xe2x88x92qxe2x88x92jLj
wherein L is at least one element selected from the group consisting of Pd, Ir, Rh, Ru and Os, and q and j satisfy the relationships (52 atomic percent)xe2x89xa6(q+j)xe2x89xa6(60 atomic percent) and (0.2 atomic percent)xe2x89xa6jxe2x89xa6(40 atomic percent).
Alternatively, the second antiferromagnetic layer may comprise an alloy represented by the formula:
PtqMn100xe2x88x92qxe2x88x92jLj
wherein L is at least one element selected from the group consisting of Pd, Ir, Rh, Ru and Os, and q and j satisfy the relationships (48 atomic percent)xe2x89xa6(q+j)xe2x89xa6(58 atomic percent) and (0.2 atomic percent)xe2x89xa6jxe2x89xa6(40 atomic percent).
According to another aspect of the present invention, a method for making a spin-valve thin-film magnetic element comprises: a laminate forming step for forming a laminate on a substrate, the laminate comprising a free magnetic layer, two nonmagnetic conductive layers formed on two surfaces of the free magnetic layer, first and second pinned magnetic layers adjoining the two nonmagnetic conductive layers, respectively, and first and second antiferromagnetic layers adjoining the first and second pinned magnetic layers, respectively, the first and second antiferromagnetic layers comprising Mn and at least one element selected from the group consisting of Pt, Pd, Ir, Rh, Ru, Os, Au, Ag, Cr, Ni, Ne, Ar, Xe and Kr; a first annealing step for annealing the laminate at a first annealing temperature while applying a first magnetic field to generate exchange anisotropic magnetic fields in the first and second antiferromagnetic layers so that the magnetization vectors of the first and second pinned magnetic layers are fixed in the same direction and so that the exchange anisotropic magnetic field of the second antiferromagnetic layer near the substrate is larger than the exchange anisotropic magnetic field of the first antiferromagnetic layer away from the substrate; and a second annealing step for annealing the laminate at a second annealing temperature higher than the first annealing temperature, while applying a second magnetic field, which is antiparallel to the first magnetic field, to fix the magnetization vector of the first pinned magnetic layer in a direction which is antiparallel to the magnetization vector of the second pinned magnetic layer.
Preferably, the magnitude of the second magnetic field is greater than that of the exchange anisotropic magnetic field of the first antiferromagnetic layer generated by the first annealing step and less than that of the exchange anisotropic magnetic field of the second antiferromagnetic layer generated by the first annealing step.
The first annealing temperature is preferably in a range of 220xc2x0 C. to 250xc2x0 C., and more preferably 220 to 240xc2x0 C.
The second annealing temperature is preferably in a range of 250xc2x0 C. to 270xc2x0 C.
The magnetization vector of the first pinned magnetic layer is fixed to be antiparallel to the magnetization vector of the second pinned magnetic layer by such a method.
In addition, the magnetization vectors of the first and second pinned magnetic layers are fixed to be antiparallel to each other while fixing the magnetization vector of the second pinned magnetic layer without deterioration of the exchange anisotropic magnetic field of the second antiferromagnetic layer. Thus, the spin-valve thin-film magnetic element produced by this method has reduced asymmetry.